Transparent mirror.



PATBNTBD FEB; 17,- 1903.

E. BLOCH.v Y

TRANSPARENT MIRRUR.

APPLIUATION FILED SEPT. 2e, 1902.

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UNITED STATES PATENT OFFICE EMIL BLOCH, OF CINCINNATI, OHIO.

TRANSPARENT MIRROR.

SPECIFICATION forming part of Letters Patent NO. 720,877, dated February17, 1903.

Application led September 26, 1902. Serial No. 124,881. (No model.)

To all whom, it may concern:

Be it known that I, EMIL BLOCH, a subject of the Emperor of Russia,residing at Cincinnati, in the county of Hamilton and State of Ohio,have invented certain new and useful Improvements in a Combined Lookingand Display Glass, of which the following is a specification.

My invention relates to an advertising display device, the features ofwhich are more fully set forth in the description of the accompanyingdrawing, forming a part of this specification, in which the figurerepresents a central vertical section of myimprovement.

A represents the frame; B, the backing-box; C, a reflector forming asupport for the electric lights D.

E represents a glass provided with a backing F, and G represents aposter or advertising plat, photograph, or work of art interposedbetween the glass and light. The backing F is formed of a composition ofmatter, but without any silver, which when applied to the back of theglass renders the glass opaque on its face under ordinary lightconditions, but transparent when a strong light is dashed in the rear.Suitable mechanism is provided for alternately operating the electriclight. When these lights are on the poster, it is shown in full outlineand color and highly illumined. When the lights are od, the glass to allappearance is an ordinary mirror. I am aware that this res ult has beenpreviously attempted by the use of the ordinary silver backing mixedWith some kind of transparent substance; but this backing isobjectionable on account of its great expense and the difficulty ofusing thensilver of suciently thin coating to render 4the glass bothopaque and transparent; also, the silver is easily destroyed and is ofvery short life when used for an advertising display device, which isalways more or less exposed and very frequentlyused as an outdoor sign.

The object of my invention is to produce a backing which will be cheapand durable and which will render the glass highly opaque to allordinary light-rays directed onto the face of the glass and clearlytransparent when the artificial lights are operated in the rear.

have found that by adding a small quantity` of potassium cyanid to themixture the backing is improved in brilliancy. I usea very smallquantity of the cyanid, generally not to exceed one-fourth part of themixture. The dierent glasses differ so materially in tensile strength,fragility, and general physical charaoteristics that it is impossible togive an exact and invariable rule of relative proportions; but with thegeneral gures I have given a skilled chemist will readily determine froma few trials what are the proper relative proportions of theconstituents of the mixture to be used for a particular purpose and witha particular glass. After this a thin coating is applied to the glasswhile hot, when it is allowed to cool, and it is preferably protected byapplying a second coating of shellac dissolved in alcohol. The secondcoating thoroughly protects the first coating. This backing isverylustrous and very durable. It adheres readily and permanently to theglass, and a coating as thin as it is possible to apply will be found toanswer all the requirements.

Having described my invention, what I claim is- A changeable mirror andtransparent glass formed of a plate of glass havinga thin coating ofRochelle salts and muriate ofl tin applied in liquid form to thebackthereof, substantially as described.

I have hereunto set In testimony whereof my hand.

` EMIL BLOCH. Witnesses:

OLIVER B. KAISER, IDA J. Locas.

